The present invention relates to purification of crude titanium tetrachloride resulting from the chlorination of titaniferous ores and more particularly to separating contaminant niobium pentachloride and tantalum pentachloride from the crude titanium tetrachloride in such process.
Chlorination of titaniferous ores produces predominantly titanium tetrachloride with a variety of contaminants usually in minor amounts, i.e. "impurity chlorides" including some oxychlorides, typically those of niobium, tin, vanadium (usually an oxychloride), tantalum, manganese, iron, zirconium, aluminum, magnesium, chromium and the like, depending upon the type and source of the ore. Typical of titaniferous ores include rutile, anatase, brookite, ilmenite and the like, often with the high iron-containing ores being first beneficiated for removal of most of the iron content of such ores. While most such contaminant chlorides can be removed by conventional condensation techniques or the like, niobium pentachloride generally cannot because of its high volatility (high vapor pressure) and high solubility in titanium tetrachloride. Also, when vaporous titanium tetrachloride is condensed to liquid titanium tetrachloride, niobium pentachloride and tantalum pentachloride condense during such operation in solid-state condition. The niobium pentachloride and tantalum pentachloride solids can be a prime cause of line-plugging in condensing systems typically located in commercial chlorination plants.
One prior proposal (U.S. Pat. No. 2,928,722) proposes to separate niobium and/or tantalum pentachloride from metal halide mixtures containing niobium and/or tantalum pentachloride and also containing iron chloride by fractional distillation wherein any anhydrous adduct of phosphorous oxychloride and aluminum chloride is added to such mixture as a fluxing agent to accomplish such fractional distillation. Similar fractional distillation and/or fractional condensation techniques for separation and recovery of various metal chlorides are well known in the art.
The present invention for separation of niobium pentachloride and tantalum pentachloride from titanium tetrachloride vehicle is based on a heretofore unknown chemical reaction phenomenon that water will preferentially react with niobium pentachloride and tantalum pentachloride rather than with titanium tetrachloride to form solid hydration products of hiobium and tantalum. By utilization of this reaction, the present invention provides a simple and economic method for purifying crude titanium tetrachloride vehicle by removing contaminant niobium pentachloride and tantalum pentachloride therefrom.